More than a little bit interesting if true... Have you ever actually heard of somebody getting a computer virus that way??
"System Tools 2011" and a few variants are know viruses. I've seen them myself on some of the customer systems that I maintain.
Viruses or Worms or whatever you want to call them are just bits of code which have been executed by the computer system. It's fairly common for bits of code such as this to be Emailed to people as attachments (which they then run), or Emailed to people as Links which they click on. Many web browsers are configured to download and execute code when they link to them. The code can be wrapped in many layers and take different forms, Flash, asp, etc, but the salient result is that they are executed on the target system. Once the code has been executed by a user of sufficient privilege the virus can embed itself anywhere in the system. MSWindows is particularly bad about this because the registry allows even users with normal permissions to make system level changes. Unix Systems are much more robust because they don't have a registry and because system level code is protected from normal users through permissions settings.
Does that answer your question?